At 05.25 hours on 23 August 1941, U-564 fired three single torpedoes at ships in convoy OG-71 about 80 miles west-northwest of Cabo Mondego, Portugal and claimed the sinking of two steamers and a corvette. However, only the loss of HMS Zinnia (K 98) (LtCdr C.G. Cuthbertson, DSC, RNR) can be confirmed from Allied sources. 17 survivors were rescued by the corvettes HMS Wallflower (K 44) (LtCdr I.J. Tyson, RN), HMS Campion (K 108) (LtCdr A. Johnson, RNVR) and HMS Campanula (K 18) (LtCdr R.V.E. Case, DSC, RD, RNR), but one died shortly after being picked up and another died in Gibraltar where the survivors were landed in the evening.